A number of methods of controlling the polymerization process of olefinic hydrocarbons in a medium of different inert solvents are known. One method disclosed in U.S. Pat. No. 3,256,262, "Measurement and Control of Mooney Viscosity in the Polymerization of Conjugated Dienes", consists of measuring the concentration of polymer in the solvent and the viscosity of the polymer solution in the polymerization system, calculating the Mooney viscosity of the obtained polymer and by its value controlling the process technological parameters.
However, the above-mentioned cannot provide sufficiently high quality of polymer required in butyl rubber production, in particular by isobutylene and isoprene copolymerization carried out in inert solvent in the presence of catalysts of aluminum chloride type (patent DDR No. 104985). The fact is that, for butyl rubber production, the molecular weight distribution (MWD) in polymer is as important as the Mooney viscosity. Besides, as a rule, butyl rubbers which have high Mooney viscosity require relatively narrow MWD while butyl rubbers which have low Mooney viscosity require a broad MWD.
It is also known that molecular weight of butyl rubber produced by in-solvent polymerization is very sensitive to process temperature. According to results of several researchers a change of process temperature of 1.degree. C. may result in a change of molecular weight of obtained polymer of up to 50,000. The above process is also characterized by a high constant of reaction rate and a high exothermic effect. For this reason rate and a high exothermic effect. For this reason the polymerization of butyl rubber in solvent is preferably carried out in a cooled reactor; for example, according to Europatent No. 53585 a reactor which has a cooling jacket plus additional cooling surface in the form of a double-wall rotating cylinder installed coaxially to the vessel body and inside of which there is an axial pump for mixing of the reaction components. As a rule, the axial pump is installed in the bottom of the vessel and the catalyst, solvent, and the monomers are also fed into the vessel at the bottom. Thus the pump performs two tasks: rapid and effective mixing of monomers and catalyst, and also a rapid displacement of reaction mass from the bottom section to prevent excessive temperature at this location which would result from the high rate and exothermicity of the reactions. The efficiency of the axial pump thus determines the uniformity of temperatures in the reactor.
It is also known that the method of controlling butyl rubber polymerization in solution which consists of controlling the rotation rate of the agitator in a reactor, in particular the axial pump in the reactor according to the above invention, depends on the temperature drop between the upper and lower sections of the vessel (USSR Author Certificate No. 1271045). However, this method also does not ensure the required quality of different grades of butyl rubber because it uses the temperature drop between the lower and upper parts of the reactor only as a method of controlling the mixing rate in the vessel and not for controlling the properties of the obtained polymer.